1. Field of the Invention
This invention relates to concrete storage tanks and in particular to concrete tanks for storing potable well water and which are susceptible to damage from accumulated sulfuric acid or residue produced when H.sub.2 S released as a gas from well water accumulates on the tank walls and inner surfaces of the roof in the area above the high water level (commonly known as the free board area) during storage.
2. The Prior Art Environment
Water drawn from wells for human consumption often contains hydrogen sulfide (H.sub.2 S) gas. Such water is known as sulfur water and it smells bad. To make the water palatable it is traditional to equip storage tanks with an aerator. The aerator is generally mounted on top of the tank and the water to be stored is pumped from the well and into the aerator where it flows by gravity into the tank itself.
The aerators used for such purposes include a series of trays and as the water flows over the trays it particulates and releases the H.sub.2 S gas. Enough H.sub.2 S remains in the water, however, so that the water in the tank continues to release H.sub.2 S into the freeboard area above the water level. When the H.sub.2 S gas contacts walls in the free board area including the underside of the concrete roof, it is converted into sulfuric acid which accumulates and attacks the concrete.
Traditionally epoxy coatings have been used to protect the concrete, and this works well as long as the coatings are in good condition. If the coatings break down or the concrete is otherwise exposed to the sulfuric acid attack, it can and does deteriorate. Moreover, for structural economy and efficiency, many prior art concrete tanks have been provided with domed roofs which are not suitable for being filled underneath with water because the water head from the highest point under the roof to the lowest point at the periphery of the roof generally is sufficient to cause the roof to lift or collapse in the absence of extremely expensive and impractical strengthening of the structure of the roof.